The present invention relates generally to the fabrication of thin films of pyrolytic carbon and, more particularly, to a method of fabricating such thin films which are characterized by an essentially uniform thickness in a range of about 0.1 to 1.0 micrometer and essentially isotropic properties.
Pyrolytic carbon has been found to be a useful material in many applications where the refractory characteristics of the material are particularly desirable and also where the isotropic strength properties of the materials are useful in unidirectional reinforcement applications. Ultra-thin films of pyrolytic carbon are especially useful where the graphite is used as a conductor in high-energy plasma generation or as a neutron getter.
Pyrolytic carbon structures including coatings and films have been satisfactorily fabricated by chemical vapor deposition procedures as are well known in the art. Various such deposition procedures are described in detail in the publication "Vapor Deposition", 1966, edited by C. F. Powell et al, and published by John Wiley & Sons, New York, N.Y. Typically, in a chemical vapor deposition process, a hydrocarbon gas in the presence of a diluent gas therefor is exposed to a substrate at a temperature sufficient to decompose the hydrocarbon gas and thereby form a coating of pyrolytic carbon on the surface of the substrate. The formation of the thin coatings or films of pyrolytic carbon on various substrate materials presents some problems when separating the vapor-deposited films from the substrates, especially the very thin films, due to the fragility of the films.
Efforts to fabricate thin pyrolytic carbon films have been somewhat successful. For example, in U.S. Pat. No. 3,900,540 which issued Aug. 19, 1975, to William A. Robba et al, films of pyrolytic carbon were fabricated by the vapor deposition of the hydrocarbon gas and its diluent onto a substrate formed of an inert liquid. The selected liquid is capable of being heated to a temperature sufficient to effect the decomposition of the hydrocarbon gas thereon for forming the pyrolytic carbon film. This film is also deposited upon parallel carbon fibers positioned over the liquid substrate so that the fibers may be utilized to pull and separate the film from the substrate. The film can be later separated from the carbon fibers and wound upon a storage drum. While this technique for fabricating thin films of pyrolytic carbon has been satisfactory for many applications, its use would be somewhat limited in the preparation of ultra-thin films having a maximum thickness of only about 1.0 micrometer. Also, the fabrication of films in seamless configurations cannot be successfully achieved due to the fixed shape of the liquid substrate in the aforementioned patent.